The invention relates to a zero-IF-converter comprising a thin-film component including at least two RC filters each comprising a resistor and a capacitor which each include a lower electrode, an upper electrode and a dielectric material.
At present, filters in zero-IF-converters for digital satellite receivers are symmetrically built up of individual capacitors and coils for the two signals of the baseband I and Q. A drawback of this construction resides in that the use of low-priced components causes the accuracy of the coils and capacitors to be reduced to a low level. As a result, the phase relationship between the signals of the baseband I and Q becomes difficult to reproduce. Consequently, expensive coils and capacitors with small tolerances must be used. In addition, the temperature dependence of the components leads to a change in the phase relationship between I and Q when the temperature drift of the components is different in both signal branches. Additionally, the manufacture, in a conventional manner, of a filter comprising discrete coils and capacitors or resistors and capacitors leads to very large dimensions.
U.S. Pat No. 5,629,655 discloses a stepwise-adjustable notch frequency filter comprising at least one input terminal and at least one output terminal and a ground terminal, a first number of resistive elements constructed as thin films deposited over a corresponding number of conducting plates with intervening dielectric layers, said resistive elements being connected in series between said at least one input and said at least one output terminal, and a second number of switches selectively arranged so as to be able to connect together certain of said conducting plates to form a resistance which is connected to said ground terminal, and means to change the value of said resistance depending on which of said conducting plates are connected together to form said resistance. The problems encountered in the mass-manufacture of said filters should be mastered by means of this arrangement.
It is an object of the invention to provide a zero-IF-converter of high quality, wherein the phase and amplitude relationship between two or more signals is very stable.
In accordance with the invention, this object is achieved by a zero-IF-converter comprising a thin-film component including at least two RC filters each comprising a resistor and a capacitor which each include a lower electrode, an upper electrode and a dielectric material, said RC filters being arranged on a common substrate. Such a zero-IF-converter is characterized by small tolerances, small dimensions and a constant amplitude and phase relationship between the base signals I and Q.
Within the scope of the invention, it is preferred that at least one RC filter is a distributed RC filter.
At least one RC filter may also be a discrete RC filter.
The upper electrode of the distributed RC filter may be resistive.
Preferably, the lower electrode of the distributed RC filter is resistive.
It may alternatively be preferred that at least one RC filter is a RC notch filter having a notch resistor.
Within the scope of the invention it is particularly preferred that at least one RC filter is a distributed RC filter, and the notch resistor is a distributed resistance component. This embodiment is characterized by a simple construction, a very good frequency characteristic and very good stability with respect to process variations.
It may be further preferred that the substrate is made of a heat-conducting material. By manufacturing the RC filters on a heat-conducting material such as Al2O3, it is ensured that the effect of temperature on the RC filters is identical.
The invention also relates to a thin-film component comprising at least two RC filters each having a resistor and a capacitor which each comprise a lower electrode, an upper electrode and a dielectric material, said RC filters being arranged on a common substrate.